This invention relates to a method of controlling fluid transfers, and more particularly, to a method for controlling fuel transfers from the fuel tanks of a distributed fuel tank system as normally found aboard an aircraft.
In an aircraft fuel system which consists of a plurality of fuel tanks, fuel lines connect the tanks to one another and to the aircraft engines. Pumps and valves (sometimes referred to herein collectively as components) are utilized to control the fuel flow, and numerous sensors are utilized throughout to monitor the system. The state (or configuration) of the control components is set to satisfy multiple criteria simultaneously. Some functions which are performed by the distributed fuel tank system are routine functions, e.g., deliver fuel to an engine. Some functions are to accommodate an abnormal condition or failure, e.g., fuel gets cold with possibility of freezing or a pump fails. Some functions are performance enhancement functions, i.e. make the aircraft operate more efficiently.
There exists a number of functions which are to be performed for a given set of conditions (i.e., climbing, on the ground, taxiing, . . . ). Further, all the functions to be performed are not necessarily compatible with one another. Thus, it is readily apparent that there can exist a situation in which some of the functions to be performed can be in "conflict" with one another, because of the limited number of resources (i.e., pumps, valves, . . . ). This "conflict" then needs to be resolved based on the current status of the aircraft, and the functions that need to be performed. Thus there exists a need to resolve the state (or sometimes referred to herein as configuration) of the pumps, valves, . . . based on the functions needed to be performed and their relative priority with the limited set of components (pumps, valves, . . . ) available. In a situation in which one fuel tank has too much fuel and another tank has too little fuel, it is desired that fuel from the one tank be transferred to the second tank such that the tanks are in balance. This situation could occur when the aircraft engines are operating or when the aircraft engines are shut down. If the situation were to occur while the engines are operating, the transfer occurs while fuel flow is maintained to the engines. Fuel tank balance is desired for a number of reasons. Maintaining the balance minimizes the stress applied to the aircraft structure. Keeping the tanks in balance assists in controlling the aircraft center of gravity, which in turn determines how efficiently the aircraft flies with the corresponding cost savings.
Present day solutions to the above identified problem are handled simply by including an additional crew member, a second officer (also known as the flight engineer), working in the cockpit to monitor the fuel system via various indicator lights and gages. At the flight engineer work station, all the switches, meters, . . . are available to permit the flight engineer to turn on/off the pumps, valves, . . . and allows the monitoring of the flow, pressures, quantities of the fuel in the system. Based on the current operating conditions, the flight engineer's knowledge of the system, and established operating procedures, the flight engineer recognizes certain conditions, e.g., the fuel tanks are out of balance. The flight engineer determines which pumps need to be turned on, which valves need to be opened, . . . in order to correct the condition. When the quantities in the tanks reach the levels desired by the flight engineer, the pumps and valves are shut down. The fuel tanks are now balanced as desired by the flight engineer. This present day system is oriented towards a human flight engineer who has detailed knowledge of the system, and extensive training and experience on how to operate the system. The flight engineer is intuitively aware of the aircraft flight regime, and is capable of interpreting all instructions from the other flight crew members or radio communications, is capable of reading and interpreting the aircraft log book, and seeks additional information and guidance from the flight crew, maintenance personnel, aircraft dispatcher, radio communications, and operating manuals when deemed necessary, and is capable of making subjective evaluations from other information available.
In order to reduce aircraft operating costs, it is desired that the crew be reduced by eliminating the flight engineer. Thus there is a need to have an automated system which performs as closely as possible the functions of the flight engineer in an automated fuel distribution system predictably, reliably, and consistently. It is understood that the use of the terms "maintaining" and "balancing" as used herein (e.g., maintaining fuel levels or balancing fuel levels in the fuel tanks) is intended to be inclusive in the overall controlling function (i.e., controlling fuel transfer) performed by the present invention.